DAR ES SALAAM, Tanzania — President Obama called on Monday for a new partnership with Africa, one that would help sustain its recent run of tremendous economic growth while broadening the rewards to as many people as possible.

“We are looking at a new model that’s based not just on aid and assistance but trade and partnership,” Mr. Obama said at a news conference with President Jakaya Kikwete of Tanzania. “Ultimately the goal here is for Africa to build Africa for Africans. Our job is to be a partner in that process.”

Mr. Obama, who arrived in Tanzania on Monday to cheering throngs much larger and louder than those he saw on the first two stops of his weeklong trip to the continent, Senegal and South Africa, acknowledged how drastically the continent had changed since his visit to Ghana four years ago. Then pictured as a desperate charity case, Africa is now seen more and more as a booming young market for the future.

“This is my final leg of my visit to Africa,” Mr. Obama said at an event with business leaders Monday night. “At every stop, one of my main messages has been that, even as this continent faces great challenges, this is also a moment of great promise for Africa.”

While Europe slips in and out of recession and appears primed for prolonged stagnation, Africa is home to many of the fastest growing economies in the world.

Economic growth for sub-Saharan Africa was a vigorous 5.1 percent last year, according to the International Monetary Fund, which predicts growth of 5.4 percent this year and 5.7 percent next year, well above expectations for the United States economy.

Trade between the United States and Africa has more than doubled over the past decade. Speaking to some 150 business leaders from the United States and Africa in Dar es Salaam on Monday night, Mr. Obama announced that Penny Pritzker, his new commerce secretary, would lead what he called a “major trade initiative” to Africa in her first year.

Mr. Obama hoped that the trip would emphasize economic partnership between the United States and Africa, but concerns about the failing health of former President Nelson Mandela of South Africa have dominated the news media’s attention.

As he searches for a legacy of his own in Africa, Mr. Obama sounded ready Monday to refocus on the vitally important issues affecting people here. Over the course of his visit, he has chosen to emphasize food security in a continent often plagued by famine and access to electricity, which two-thirds of Africans live without.

Mr. Obama has unveiled an ambitious program to double access to electricity in sub-Saharan Africa, investing $7 billion in financial support for an initiative called “Power Africa.” Tanzania is one of the initial six participating countries where the government hopes to add 10,000 megawatts of generation capacity and reach 20 million households that lack electricity right now.

For Mr. Obama, the push to improve trade, investment and power in Africa is unlikely to draw big headlines or provide the president with a flashy legacy on the continent. But White House officials argue that over the long term, success in their efforts could have a huge impact on improving the lives of Africans and increasing the fortunes of American companies.

“While they may not have the immediate symbolism and very intense call to action that something like the Berlin Wall had, or of course apartheid did,” said Benjamin J. Rhodes, the deputy national security adviser, “we need to recognize that there is still a significant amount of work to do in the years ahead.”

Throughout his stay, Mr. Obama’s agenda for Africa has been compared to that of his predecessor, George W. Bush, who invested billions of dollars to try to eradicate AIDS on the continent. Mr. Obama praised the program but said his administration had expanded the idea to treat even more diseases.

The military band for the Tanzania People’s Defense Force greeted Mr. Obama by playing the United States national anthem twice. Cannons repeatedly punctuated the songs with huge blasts in the air. A yellow banner with Mr. Obama’s picture said, “President Obama, Welcome to Tanzania,” in Swahili.

A sea of ecstatic Tanzanians welcomed Mr. Obama, the first American president with family roots in Africa. They lined nearly every inch of the streets as his motorcade made the 20-minute journey to the Tanzanian state house. The crowds, a dozen rows deep in some places, roared with approval as Mr. Obama passed.

One man dressed in an American flag shirt pumped his fists into the air exuberantly as the president drove by.

Ten men crowded around a single handset at Yasir Ahmed Hardware, taking a break from building wooden doors and metal grates to watch Mr. Obama’s arrival. “All we need Obama to help us with is a consistent, reliable supply of electricity,” said Alex Adrian, 32, a carpenter.

The men at the workshop, which employs 35 workers, said that the power goes out for several hours two to three times a week. The men said that they made roughly $12 to $18 a day, but that when the power went down they could not work, meaning they and their families had to skip meals. The workers said they did not have electricity at home and used kerosene lamps in the evening.

Asked whether the United States was doing enough for Tanzania, Mr. Kikwete offered high praise, but joked that he would not say that Americans were doing enough. “The U.S. is doing a lot, but if I say the U.S. has done enough, the president won’t listen to my new requests,” he said, prompting laughter from the audience and Mr. Obama. “But so far, so good.”

Mr. Obama said that for two-thirds of sub-Saharan Africans to lack power was “unacceptable in 2013.”

“We can’t have a seven-year time frame for building a power plant,” Mr. Obama said. “We have to move. Things have to go faster.”

Without a more aggressive push on Africa, the United States also risks falling even further behind China in the fast-growing region. China has expanded its role significantly while the United States has seemed distracted by its military ventures both here and elsewhere.

China’s new president, Xi Jinping, visited Dar es Salaam in March on his first tour abroad as the country’s leader. Trade between the United States and Tanzania last year totaled $360.2 million, compared with $2.47 billion between China and Tanzania.

Mr. Obama also announced a new push to prevent wildlife trafficking, in which sophisticated poaching syndicates kill elephants and rhinoceroses and sell their tusks and horns in contravention of international conventions. Mr. Obama committed $10 million to help combat the problem and will detail a member of the federal Fish and Wildlife Service to the continent.

“It’s decimating the populations of some of Africa’s iconic animals, including rhinoceros and elephants as well,” said Grant Harris, the senior director for Africa on the National Security Council. “One thing we have been doing so far is raising the global profile of how bad this issue is,” Mr. Harris said, adding that the United States would continue “a massive diplomatic campaign” to make other countries more aware of the issue.

White House officials also said Monday that Mr. Obama would be joined by Mr. Bush, at a wreath-laying event Tuesday morning at the site of one of the 1998 coordinated bombings of United States Embassies in Tanzania and Kenya. Ten people were killed at the embassy in Dar es Salaam.